some programs!

graph/USACO06DECs_cow_picnic.cpp

@@ -0,0 +1,83 @@
+#include <cstring>
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+class Graph {
+public:
+    struct Edge {
+        int target_vertex = -1;
+        int next_edge = -1;
+    };
+
+    vector<int> head_edges;
+    vector<Edge> edges;
+
+    explicit Graph(int vertices_amount = 0, int edges_amount = 0) : head_edges(vertices_amount, -1) {
+        edges.reserve(edges_amount);
+    }
+
+    void init(int vertices_amount, int edges_amount) {
+        head_edges.resize(vertices_amount, -1);
+        edges.reserve(edges_amount);
+    }
+
+    void add_edge(int source_vertex, int target_vertex) {
+        edges.push_back({target_vertex, head_edges[source_vertex]});
+        head_edges[source_vertex] = static_cast<int>(edges.size()) - 1;
+    }
+};
+
+constexpr int MAX_V = 1e3 + 5;
+
+int cows_amount, vertices_amount, edges_amount, ans;
+vector<int> cows_locations;
+Graph graph;
+
+bool vis[MAX_V];
+int vertices_accessibility[MAX_V];
+
+void dfs(int start_vertex, int current_vertex) {
+    if (vis[current_vertex]) { return; }
+    vis[current_vertex] = true;
+    vertices_accessibility[current_vertex]++;
+    for (int edge = graph.head_edges[current_vertex]; edge != -1; edge = graph.edges[edge].next_edge) {
+        int next_vertex = graph.edges[edge].target_vertex;
+        dfs(start_vertex, next_vertex);
+    }
+}
+
+void dfs(int start_vertex) {
+    memset(vis, false, sizeof(vis));
+    dfs(start_vertex, start_vertex);
+}
+
+int main() {
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> cows_amount >> vertices_amount >> edges_amount;
+    cows_locations.resize(cows_amount);
+    graph.init(vertices_amount, edges_amount);
+    for (int i = 0; i < cows_amount; i++) {
+        cin >> cows_locations[i], cows_locations[i]--;
+    }
+    for (int i = 0; i < edges_amount; i++) {
+        int source_vertex, target_vertex;
+        cin >> source_vertex >> target_vertex, source_vertex--, target_vertex--;
+        graph.add_edge(source_vertex, target_vertex);
+    }
+
+    for (const int cow : cows_locations) {
+        dfs(cow);
+    }
+    for (int i = 0; i < vertices_amount; i++) {
+        if (vertices_accessibility[i] == cows_amount) {
+            ans++;
+        }
+    }
+    cout << ans << endl;
+
+    return 0;
+}